Author Topic: Traffic light circuit with 556 timer?  (Read 10389 times)

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Offline phennesseyTopic starter

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Traffic light circuit with 556 timer?
« on: December 20, 2019, 08:52:52 pm »
Disclaimer: this is my first electronics project ever. I understand basic electronic components and how they work, but I've never built anything in my life. I thought this project was a good starting point.

I want to build the following "traffic light" circuit that uses two 555 timers to light up three LEDs in sequence:



But...I want to use a dual 556 timer instead of two 555 timers. I attempted to re-draw this circuit with the correct pinouts and removed the extra in/out lines. I don't think I did it right...can anyone help me redraw this so that it would work with a single 556 IC?

Some info on the pinouts for the 555 and 556:
https://dlb.sa.edu.au/rehsmoodle/file.php/466/kpsec.freeuk.com/555timer.htm

Also, would it be a bad idea to build this thing on a mini 170-pin breadboard with no power rails? Is there enough room on one of those to build this?

Thanks for any help you can provide!
« Last Edit: December 20, 2019, 09:55:50 pm by phennessey »
 

Offline Wimberleytech

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Re: Traffic light circuit with 556 timer?
« Reply #1 on: December 20, 2019, 10:57:59 pm »
Disclaimer: this is my first electronics project ever. I understand basic electronic components and how they work, but I've never built anything in my life. I thought this project was a good starting point.

I want to build the following "traffic light" circuit that uses two 555 timers to light up three LEDs in sequence:

(Attachment Link)

But...I want to use a dual 556 timer instead of two 555 timers. I attempted to re-draw this circuit with the correct pinouts and removed the extra in/out lines. I don't think I did it right...can anyone help me redraw this so that it would work with a single 556 IC?

Some info on the pinouts for the 555 and 556:
https://dlb.sa.edu.au/rehsmoodle/file.php/466/kpsec.freeuk.com/555timer.htm

Also, would it be a bad idea to build this thing on a mini 170-pin breadboard with no power rails? Is there enough room on one of those to build this?

Thanks for any help you can provide!

It would be instructive for you to try to figure this out on your own.  It is easy to map the functions of the pins to their respective pins.
You need to put a bypass capacitor across the supply pins (not shown in your schematic).  Post your result and I or someone else will check your work.

There may be enough room to build it but you need to try to figure that out.  Download a copy of Fritzing and build it there first.  You can optimize placement and know ahead of time if there is enough room.
 

Offline james_s

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Re: Traffic light circuit with 556 timer?
« Reply #2 on: December 21, 2019, 12:19:39 am »
The 556 has exactly the same pins as a pair of 555s except there is only one set of power and ground pins. What aspect is confusing you? Draw it up to the best of your ability and share that drawing and we can help you figure out anywhere you went wrong.
 

Offline schmitt trigger

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Re: Traffic light circuit with 556 timer?
« Reply #3 on: December 21, 2019, 12:50:37 am »
I can see where his confusion is.
The left 555 powers up via its output (pin 3) the right 555's Vcc input (pin 8   ).

This circuit cannot be implemented with a 556, which share a common Vcc input.

But even then, the circuit's operation is suspect. How does the circuit cycle back to the red light once that the green times out? There is no signal feedback from right to left.
 
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Offline phennesseyTopic starter

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Re: Traffic light circuit with 556 timer?
« Reply #4 on: December 21, 2019, 01:32:10 am »
Thank you! I thought I was taking crazy pills.

Is there a way to wire three LEDs to a single 556 that would produce the same effect?
 

Offline Wimberleytech

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Re: Traffic light circuit with 556 timer?
« Reply #5 on: December 21, 2019, 02:32:53 am »
I can see where his confusion is.
The left 555 powers up via its output (pin 3) the right 555's Vcc input (pin 8   ).

This circuit cannot be implemented with a 556, which share a common Vcc input.

But even then, the circuit's operation is suspect. How does the circuit cycle back to the red light once that the green times out? There is no signal feedback from right to left.

Derp...good catch.  I did not notice that!
 

Offline schmitt trigger

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Re: Traffic light circuit with 556 timer?
« Reply #6 on: December 21, 2019, 06:15:45 pm »
Traffic lights are classic classroom example when learning about state diagrams and/or truth tables.
I have made a fictional intersection in a pair of streets: Second avenue and Main street. Please check the attached Excel spreadsheet.

To keep things simple, I've arbitrarily made them one way, and have not included turn signals.

The circuit has four states, which repeat endlessly and six outputs, one each for each light color on a street.
Fortunately, four states can be realized with a two bit counter, with a single IC dual flip flop like the CD4013.
 
Then using sums of minterms, you decode each output. For instance, the Second ave green light is simply A * B/

The fact that the yellow light has a different duration than the other lights complicates things a little, but with additional steering logic you could change your astable's time constant.

Of course, doing this with a microcontroller is trivial.
 

Offline james_s

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Re: Traffic light circuit with 556 timer?
« Reply #7 on: December 21, 2019, 06:27:10 pm »
Wow I didn't even notice the second IC was powered by the first, that's quite a strange way of implementing a traffic light.
 

Offline rstofer

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Re: Traffic light circuit with 556 timer?
« Reply #8 on: December 21, 2019, 06:52:52 pm »
Traffic lights are classic classroom example when learning about state diagrams and/or truth tables.
I have made a fictional intersection in a pair of streets: Second avenue and Main street. Please check the attached Excel spreadsheet.
In the US, the 'warn' signal is never given.
« Last Edit: December 21, 2019, 06:54:36 pm by rstofer »
 

Offline james_s

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Re: Traffic light circuit with 556 timer?
« Reply #9 on: December 21, 2019, 07:17:13 pm »
As one of the small minority of people who still insists on a proper manual gearbox I've often wished it was. Seems like a handy feature that has never been implemented in this part of the world.
 

Offline rstofer

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Re: Traffic light circuit with 556 timer?
« Reply #10 on: December 21, 2019, 08:06:10 pm »
As one of the small minority of people who still insists on a proper manual gearbox I've often wished it was. Seems like a handy feature that has never been implemented in this part of the world.

Well, in the '60s, we would have used it to put torque on the rear wheels in anticipation of getting the green light.  Street racing...

I first encountered it when I was stationed in Germany.  I thought it was a very efficient way to tell people it was just about time to go.  I wonder how many T-bone accidents it facilitates.
 

Offline james_s

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Re: Traffic light circuit with 556 timer?
« Reply #11 on: December 21, 2019, 08:10:55 pm »
I haven't ever bothered to look at any statistics on that. I've formed a habit of looking at the cross street signals if I can see them and when those turn yellow I put my car in gear. I like having a warning so I'm not either holding the clutch down the whole time I'm sitting there, or abusing the 1st gear synchro by stuffing it into gear to go before the guy behind me has a fit.
 

Online Zero999

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Re: Traffic light circuit with 556 timer?
« Reply #12 on: December 21, 2019, 09:54:31 pm »
The sequence seems to differ the world over.

In the UK it's:
Red
Red & Amber
Green
Amber
Red


What sequence does the original poster require?

If it's just sequentially lighting the LEDs one after the other, just use a ring oscillator. Here's an example which can be built with the 74HC14.
« Last Edit: December 21, 2019, 11:40:32 pm by Zero999 »
 

Offline schmitt trigger

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Re: Traffic light circuit with 556 timer?
« Reply #13 on: December 22, 2019, 01:50:59 am »
The sequence seems to differ the world over.

What sequence does the original poster require?



Exactly,
That is the reason I suggested to the OP that he must construct a truth table listing all the states on all the roads.

But perhaps he only requires to build a ring oscillator, just like you indicated.
 

Offline phennesseyTopic starter

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Re: Traffic light circuit with 556 timer?
« Reply #14 on: December 22, 2019, 01:53:34 am »
Red, green, yellow. That simple. Timing: Red and green for longer, yellow shorter.

I’m trying to use only a 556 timer and the components listed in the diagram. Can it be done? I already ordered these components from Digikey...honestly just hoping there’s a way to do it with them. My goal is to use as few components as possible!
« Last Edit: December 22, 2019, 01:57:28 am by phennessey »
 

Offline schmitt trigger

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Re: Traffic light circuit with 556 timer?
« Reply #15 on: December 22, 2019, 05:14:31 am »
The exact same diagram, with a single 556?

Short answer; No. For the reason I provided in post #4.

Perhaps instead of powering the second timer, you could manipulate the reset. Which the 556 will have two independent resets.
« Last Edit: December 22, 2019, 05:16:46 am by schmitt trigger »
 

Offline SmokeyTheElectrician

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Re: Traffic light circuit with 556 timer?
« Reply #16 on: December 22, 2019, 02:14:42 pm »
Disclaimer: this is my first electronics project ever. I understand basic electronic components and how they work, but I've never built anything in my life. I thought this project was a good starting point.

I want to build the following "traffic light" circuit that uses two 555 timers to light up three LEDs in sequence:

(Attachment Link)

But...I want to use a dual 556 timer instead of two 555 timers. I attempted to re-draw this circuit with the correct pinouts and removed the extra in/out lines. I don't think I did it right...can anyone help me redraw this so that it would work with a single 556 IC?

Some info on the pinouts for the 555 and 556:
https://dlb.sa.edu.au/rehsmoodle/file.php/466/kpsec.freeuk.com/555timer.htm

Also, would it be a bad idea to build this thing on a mini 170-pin breadboard with no power rails? Is there enough room on one of those to build this?

Thanks for any help you can provide!

You are actually very close to having that circuit right.
For the 555 on the right side, you must have gotten
scrambled up 'cause:
a) the Orange LED circuit high side should come from the left side 555's output ( not 12 volts)
b) pin 8 for the right side 555 should go to 12 volts ( not the left side 555's output )
c) pin 4 for the right side 555 should go to the left side 555's output ( not 12 volts )

I think that should do it.
Let us know how it works out for you,
or if you could use more help.
( post circuits, drawings, wave forms, both from simulation and IRL )

BTW if the right side circuit was in the configuration where you could set the duty cycle,
you would be able to get the periods of the red cycle and green cycle to match almost
exactly -- refer to figure 14 on page 10 in TI's 555 Datasheet - https://www.ti.com/lit/ds/symlink/lm555.pdf.

good luck
and
cheers to all



"We must stick them with quills! It's the only way!"
-- Scott Adams
 
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Offline SmokeyTheElectrician

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Re: Traffic light circuit with 556 timer?
« Reply #17 on: December 22, 2019, 02:38:00 pm »
I can see where his confusion is.
The left 555 powers up via its output (pin 3) the right 555's Vcc input (pin 8   ).

This circuit cannot be implemented with a 556, which share a common Vcc input.

But even then, the circuit's operation is suspect. How does the circuit cycle back to the red light once that the green times out? There is no signal feedback from right to left.

The timer on the left just free runs.
The timer on the right has a period long enough that it does not quite fit in a half cycle of the first.
I do not know the  OP's source for the circuit, but after realizing the above, it seemed the idea
was to hold the right side timer in reset for half of a cycle of the left side timer and then let
it run during the left side timer's other phase (output high). I think if the right hand circuit
would have been a one shot, the design would have been easier to decipher...

Cheers to all
"We must stick them with quills! It's the only way!"
-- Scott Adams
 

Offline ebastler

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Re: Traffic light circuit with 556 timer?
« Reply #18 on: December 22, 2019, 03:03:05 pm »
My goal is to use as few components as possible!

That would be a small microcontroller. 8-pin DIP, 6 I/O pins -- just enough for the lights at both crossroads. You need just the single chip, plus LEDs and series resistors. (If you use a star network, that's just one package for the resistors too.)  And you can implement any signal sequence and timing you like.

I realize that you may want to do this with 555s as an intellectual exercise. But a microcontroller is really the way to go for a practical implementation.
 
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Offline phennesseyTopic starter

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Re: Traffic light circuit with 556 timer?
« Reply #19 on: December 22, 2019, 06:27:27 pm »
No, not the same diagram. I mean the same components. Can these components produce the effect?

556 timer
2x 100uF caps
5x resistors with the values listed
3 LEDs blinking in sequence (Gr long, Yl. short, Rd. long)
 

Offline james_s

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Re: Traffic light circuit with 556 timer?
« Reply #20 on: December 22, 2019, 06:59:26 pm »
I don't see how. You'd need to add at least something to allow you to hold the second timer in reset and also prevent either LED from lighting while the first one is on. As I mentioned earlier, this is an unusual way of doing a traffic light.
 

Offline phennesseyTopic starter

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Re: Traffic light circuit with 556 timer?
« Reply #21 on: December 22, 2019, 07:35:22 pm »
Besides a microcontroller, what’s a single simple IC that could do this? There are many 555 variants out there (like the 556), would any of those achieve this effect?
 

Offline james_s

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Re: Traffic light circuit with 556 timer?
« Reply #22 on: December 22, 2019, 07:49:04 pm »
Well you could use a pair of 555's as done in the original circuit. There's also the classic design using a decade counter and some diode 'or' logic. http://nickviera.com/electronics/traffic_simple/

Countless other ways of achieving the same thing, most will start with something like a 555 to generate pulses and then some sort of counting logic.
 

Offline phennesseyTopic starter

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Re: Traffic light circuit with 556 timer?
« Reply #23 on: December 22, 2019, 08:13:20 pm »
Yes, but those use multiple ICs. Is there a single IC, besides a microcontroller, that can achieve this?
 

Online Zero999

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Re: Traffic light circuit with 556 timer?
« Reply #24 on: December 22, 2019, 09:02:40 pm »
Yes, but those use multiple ICs. Is there a single IC, besides a microcontroller, that can achieve this?
The schematic I posted previously can do it using a single IC, such as the 74HC14. Which pin goes where should be apparent when you've read the data sheet. Obviously the power pins 7 and 14 will need to be connected to 3V to 6V, with a 100nF decoupling capacitor across them.
https://www.mouser.com/datasheet/2/308/74HC14.REV1-34947.pdf

If you must use the 555 timer, you can use them as Schmitt triggers to make the same circuit as I previously posted, but will need two or three ICs.
 
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